The Génis Unit is a Paleozoic metasedimentary succession of the southern Limousin and belongs geologically to the Variscan basement of the French Massif Central. The unit covers the age range Cambrian/Ordovician till Devonian. Type locality The Génis Unit was named after its type locality, the small town Génis, situated in the northeastern Dordogne. Geographical Occurrence The Génis Unit occurs in an elongated strip at the northeastern edge of the Dordogne department, following a WNW-ESE direction for about 26 kilometres. Its width across strike is not more than 5 kilometres. The unit forms part of the Bas Limousin, a basement plateau that was peneplained during the Paleogene. The plateau's elevation oscillates between 300 and 400 meters. Geologically the unit's northern limit is the South Limousin Fault, a very important ductile, dextral wrench fault separating the Génis Unit from the Thiviers-Payzac Unit to the north. To the south the unit is overlain by liassic sediments of the Aquitaine Basin. In the east the group disappears beneath Permian red beds of the Brive Basin. Its sedimentary succession can be best studied along the Auvézère river. Comparable units to the Génis Unit with an identical stratigraphic succession can be found in the Vendée and in the Rouergue. Stratigraphy The Génis Unit shows the following stratigraphic succession (from top to bottom): Génis greenschist Génis sericite schist Puy-de-Cornut arkose Génis porphyroid Génis greenschist The Génis greenschist is the youngest formation of the Génis Unit. The greenschist derives from mafic magmatic rocks like gabbro and basaltic pillow lava, basic volcanoclastics and rare intercalations of chert and pelite. A lower Devonian age can be attributed to the greenschist. Incorporated at the base of the greenschist are limestone lenses containing upper Silurian conodonts. Génis sericite schist The underlying Génis sericite schist is very rich in the minerals quartz, chlorite and muscovite (variety sericite). The sericite schist is probably of Ordovician and lower Silurian age (rare finds of Ordovician acritarchs have been made). Puy-de-Cornut arkose Below the Génis sericite schist follows the Puy-de-Cornut arkose. The arkose is strongly silicified and forms erosionally resistant morphological ridges. It is supposed to be an equivalent of the Puy-des-Âges quartzite from the neighbouring Thiviers-Payzac Unit. A close relationship with the Grès Armoricain in Brittany is also considered. Therefore an Ordovician age of the arkose is most likely. Génis porphyroid Below a pronounced angular unconformity one encounters the Génis porphyroid. This rock represents alkaline, rhyolitic